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Abstract: Research is increasingly focusing on the incorporation of electromechanical actuators into future More Electric Aircraft. For an actuator to be feasible in a commercial aircraft, the most critical design factor is attaining the strict safety requirements. The electrical drives used in More Electric technologies must also be suitable for the conventional power supply and control arrangements of aircraft, otherwise feasibility of a new technology may be reduced. This study discusses the generic design requirements for electromechanical actuators from a safety perspective, including the application of fault-tolerant electric drives. Later, two prototype electromechanical actuators, developed by the authors are discussed, comparing the different topologies.
1 Actuation systems in commercial aircraft
A reduction of weight in an aircraft can result in reduced fuel consumption or an increased payload. Conventionally the 'secondary power systems of aircraft - that is, actuation, avionics, galley supplies, air conditioning and wing de-icing, are powered from hydraulic, electrical and pneumatic supplies. Studies in the 1980s suggested that with all supplies sized for their peak power requirements, but under-utilised for majority of flight, a weight reduction could be achieved by migrating all systems to electrical supplies for load sharing and a smaller power generation system [1], More Electric Aircraft initiatives have driven a series of projects concerned with increasing the proportion of electrically powered systems on commercial aircraft, particularly focussing on electrical alternatives to hydraulic actuation and optimising the electrical power systems.
The A380 has demonstrated some of the recent More Electric actuator developments with electro-hydrostatic actuators (EHA) present on the ailerons and elevators, and electrical back-up hydraulic actuators (EBHA) present on the rudder and spoilers. The EHA and EBHA are both hydraulic actuators in nature, with the EHA using an electrical supply to drive an internal pump to hydraulically actuate a surface from an internal reservoir [2]. The EBHA operates from a conventional hydraulic supply but features a similar system to the EHA as a safety backup. While both actuators allow a reduction in the quantity of hydraulic power supplies required on an aircraft, the majority of actuation remains purely hydraulic in the A380. A similar power-by-wire arrangement is intended for the Boeing 787 with electrically driven pumps pressurising localised hydraulic supplies for hydraulic actuators.
The EHA and EBHA could...